<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		*{padding: 0;margin: 0;}
		
		html,body{
			height: 100%;
		}
		/* 第一种布局 */
		.wrapper{
			display: flex;
			height: 100%;
			width: 100%;
		}
		.side-box{
			width: 200px;
			background: #ccc;
		}
		.main-box{
			flex: 1;
			background: #f5f5f5;
		}
	</style>
</head>
<body>
	<div class="wrapper">
		<div class="side-box">200px</div>
		<div class="main-box">自适应</div>
	</div>
</body>
</html>